posted on 2023-01-09, 16:07authored byJulie-Ann Hoffman, Ziba S. H. S. Rajan, Darija Susac, Mangaka C. Matoetoe, Rhiyaad Mohamed
The
widespread implementation of proton exchange membrane water
electrolyzers (PEMWEs) is greatly hindered by the availability and
high costs associated with key catalyst and electrode components.
The anodic oxygen evolution reaction (OER) is known to be kinetically
challenging and therefore requires substantially high loadings of
Ir-based catalysts (∼2 mg cm–2). A promising
strategy to lower the amount of iridium is to enhance the electrocatalytically
active surface area, by means of dispersing finely divided nanoparticles
of iridium/iridium oxide over cheaper, electronically conductive,
stable oxide support materials. In this work, we use a metal–organic
chemical deposition (MOCD) technique to deposit IrOx (x = 0–2) nanoparticles on tin-doped
indium oxide (ITO) supports with different physicochemical properties
such as specific surface area and Sn dopant concentration. The MOCD
technique has been proven to deliver catalysts with well-dispersed
nanoparticles and narrow particle size distributions. This approach,
in combination with the chosen ITO supports, allows for decoupling
of particle size and Ir loading effects from other catalyst–support
interactions that are contributing to catalyst activity, stability,
and nature of deposited nanoparticles. In this way, we were able to
investigate the effect of IrOx nanoparticle
coverage effects on ITO and found that high nanoparticle coverage,
i.e., low interparticle distances of the IrOx nanoparticles supported on low surface area ITO, increased
the stability of the support. The specific surface area of ITO supports
was found to correlate with the nature of surface Sn and In species,
which in turn influenced the nature of deposited IrOx nanoparticles for enhanced OER activity. The most stable OER
catalyst had highly dispersed, small (2.4 ± 0.7 nm), predominantly
metallic Ir nanoparticles with a high mass-specific OER activity of
207 ± 34 A gIr–1 at 1.525 V vs RHE.
This was obtained by the interplay of the Ir phase, optimized for
improved activity and low interparticle distance for catalyst stability.